In various industries or arts, it is necessary, as part of the overall process, to dry a continuous sheet or strip of material. For example, in the art of paper-making, the relatively wet or damp strip or web of paper fibers is often passed over and mostly about a rotatable drum or cylinder assembly which is heated in order to thereby evaporate the moisture of the wet or damp paper sheet in contact with and passing about the outer cylindrical surface of such rotatable drum or cylinder asssembly.
The prior art has employed steam for the heating of such rotatable drying drums or cylinder assemblies. More specifically, heretofore, the prior art has employed a drying cylinder or drum assembly comprised of a cylindrical shell having axially closed end-walls defining an inner chamber into which, as through the axis of rotation in an end wall, steam is supplied in order to sufficiently heat the cylindrical shell, and the outer cylindrical surface thereof, and thereby achieve the desired degree of drying of the paper sheet or material passing in contact with the said outer cylindrical surface.
The steam thusly admitted into the inner chamber of the drying cylinder or drum assembly, upon giving-up some of its heat, forms a condensate within said inner chamber and, obviously, such condensate must be removed in order to maintain a continuous drying process.
One type of drying cylinder, thusly heated by steam, comprises a plurality of circumferential grooves on the internal surface of the cylinder shell in which condensate collects and at least one condensate collection pipe or conduit for removing condensate from the drying cylinder wherein such collection pipe extends transversely across said circumferential grooves and to which suction pipes or conduits extending into said grooves are connected. Such type of drying cylinder has heretofore become known from Federal Republic of Germany Patent Specification No. 23-38-922 which is equivalent to United Kingdom Letters Patent No. 1,473,419 and U.S. Pat. No. 3,914,875.
In such type of prior art drying cylinder it is particularly important that heat transmission through the cylinder wall is equal in all zones of the outer cylindrical surface or shell face. This presupposes that in particular, the thickness of the film of condensate formed in said circumferential grooves is uniform over the entire circumference. However, as a result of the suction effect this is not the case directly in the vicinity of the condensate suction pipes which project into the circumferential grooves. There the film of condensate or the flow of condensate, respectively, is thinner. Heat transmission is therefore significantly higher at these points.
According to said Patent Specification No. 23-38-922, inserts are provided in the grooves and the purpose of these is to produce turbulence in the film of condensate. The problem is somewhat alleviated by this but not completely solved.
The invention as herein disclosed is primarily directed to the solution of the problem of uneven heating of the cylinder shell face of such prior art drying cylinder.